US TBS six classification reporting system. Class I. The specimen is not diagnostic or unsatisfactory. It mainly refers to the low number of cells suitable for microscopic observation, which is related to puncture operations and smear fixation. The risk of malignancy in this category is about 1-4% and accounts for <10% of the diagnosis. repeat ultrasound-guided fine needle aspiration after 3 months usually yields a definitive diagnosis. Category II, benign lesions. Most common (>60%), benign follicular and inflammatory cells are usually seen microscopically, with a risk of malignancy of approximately 0% to 3%. Patients in this category require only follow-up (6 to 18 months interval) and do not require surgery. Category III, atypical cellular lesions/follicular lesions of unknown significance. Microscopic cells appear atypical but are not sufficient for diagnosis of categories IV, V and VI. The risk of malignancy in this category is approximately 5% to 15% and cannot be overdiagnosed. The management of such patients is to repeat the fine needle aspiration after 3 months, and most of the second aspiration diagnoses are definitive and benign. Class IV (suspicious) follicular tumors. Microscopically it is predominantly microfollicular or eosinophilic. The risk of malignancy in this category is about 15%-30%, and its benign and malignant judgment mainly depends on postoperative pathological examination, and cytologic diagnosis only plays a screening role. Multidisciplinary discussion is recommended to determine the treatment plan, and lobectomy of the thyroid gland is feasible. Class V, suspicious malignant tumor. The risk of malignancy is 60%-77%. Intraoperative cryo-examination can be performed to determine the diagnosis and select a major or total thyroidectomy. Category VI, malignant tumors. The risk of malignancy in this category is 97% to 99%. Cytology can diagnose a variety of malignancies, more than 95% of which are papillary carcinomas. Management is either a major or total thyroidectomy.